According to OSSF rules, where does more treatment of wastewater occur?

The correct answer is that more treatment of wastewater occurs in the soil. In an On-Site Sewage Facility (OSSF), wastewater first undergoes primary treatment in the septic tank. This involves the separation of solids from liquids, where bacteria break down some of the organic material. However, the majority of treatment takes place in the soil, which acts as a natural filter.

As the effluent from the septic tank is dispersed into the soil, various physical, chemical, and biological processes further treat the wastewater. Soil microorganisms play a crucial role by breaking down remaining organic matter, pathogens, and other pollutants. The soil's structure and composition facilitate the adsorption and natural decomposition of harmful substances, significantly enhancing the treatment efficacy before the effluent reaches groundwater or surrounding water bodies.

While leach fields are an integral part of this process as they distribute the effluent into the surrounding soil, the broader treatment mechanism occurs throughout the soil surrounding the leach field. Sewer lines, on the other hand, are primarily involved in transporting wastewater to treatment facilities and do not contribute to treatment. Therefore, the most accurate answer reflecting where substantial treatment occurs is indeed in the soil.